1. Field of the Invention
The present invention relates to an automobile headlamp such as dual-lamp halogen headlamp, that provides a predetermined low beam light distribution pattern and a high beam light distribution pattern by means of control of all-surface reflection light distribution of the reflecting surface, and particularly to an automobile headlamp that makes it possible to utilize near 100% of light incident on the reflecting surface of a reflector and to obtain good low beam light distribution pattern and high beam light distribution pattern.
The word "ahead" used in this specification refers to the direction in which the automobile moves, that is the forward direction in view of the driver. Letter "L" used in the accompanying drawings indicates the left-hand side in view of the driver looking ahead, and letter "R" used in the accompanying drawings indicates the right-hand side in view of the driver looking ahead. Letter "U" used in the accompanying drawings indicates the upper side in view of the driver looking ahead, and letter "D" used in the accompanying drawings indicates the lower-hand side in view of the driver looking ahead. Letters "HL-HR" used in the accompanying drawings indicate a horizontal line (or a horizontal axis) viewed by the driver looking ahead, and letters "HR-HL" used in the accompanying drawing indicate a horizontal line (or a horizontal axis) when viewing the automobile (or the surface that includes headlamps) from the front side (the so-called front view or plan view), and letters "VU-VD" indicate the vertical line (or a vertical axis).
2. Description of the Prior Art
Automobile headlamps of this type, namely automobile headlamps that make it possible to obtain a predetermined low beam light distribution pattern and high beam light distribution pattern by means of control of all-surface reflection light distribution of the reflecting surface include, for example, one that is disclosed in Japanese Unexamined Patent Publication No. Hei 8-329703.
This automobile headlamp will be described below with reference to FIG. 15 through FIG. 24. Further, the automobile headlamp shown in the drawings is to be mounted on the left side (left-hand side in view of the driver facing ahead) of an automobile in keep-right traffic. In the case of an automobile headlamp mounted on an automobile in keep-left traffic, the automobile headlamp, a reflecting surface 40, a high beam filament 52 and other devices are disposed in a reverse arrangement to that shown with regard to right and left. Further, the automobile headlamp to be mounted on the right side of the automobile has a lamp housing 1, a lens 2 and a reflector 4 of substantially symmetrical configuration as those of the automobile headlamp shown, without any change in the arrangement of the reflecting surface 40, the high beam filament 52 and other devices.
The automobile headlamp has a light room 3 formed by the lamp housing 1 and the lens (outer lens) 2. Disposed in the light room 3 is a reflector 4, which is separate from the lamp housing 1, to be capable of swinging in the vertical and horizontal directions by means of a pivot mechanism (not shown) and an optical axis adjusting device (not shown). The reflector 4 has the reflecting surface 40 formed from a complex reflecting surface. The reflecting surface 40, namely the complex reflecting surface, comprises a plurality of reflecting surface segments (not shown) divided vertically and horizontally, and is called the free curved surface. The free curved surface may be, as described in Japanese Unexamined Patent Publication No. Hei 9-306220, for example, one divided into a multitude of blocks, one divided into a small number of blocks, or one comprising a plurality of blocks continuously connected (joints between the blocks not being visible).
Although the complex reflecting surface does not have a single focal point in the exact sense of the word, there are only negligible differences between the focal lengths of the plurality of revolving paraboloid surfaces that form the complex reflecting surface. Thus because the plurality of revolving paraboloid surfaces share substantially the same focus, the focal point F shown in the drawing that is a pseudo-focus in the true meaning will be called the focal point in this specification. Similarly, the optical axis Z--Z shown in the drawing that is a pseudo-optical axis in the true meaning will be called the optical axis in this specification.
The reflector 4 described above has a light source bulb 5 mounted thereon detachably. The light source bulb 5 is a light source bulb without a shading hood, and has a low beam (beam for passing oncoming vehicle) filament 51 and a high beam (beam for running without oncoming vehicle) filament 52 disposed in the glass bulb 50. Also the glass bulb 50 has a coating 54 (for blocking the light from the low beam filament 51 and from the high beam filament 52 from directly entering the lens 2) of black paint, for example, provided at the tip thereof.
The low beam filament 51 described above has a substantially cylindrical shape, disposed substantially in parallel with the optical axis Z--Z at a position ahead of the focal point F. The high beam filament 52 also has a substantially cylindrical shape, disposed substantially in parallel with the optical axis Z--Z at a position near the focal point F and obliquely below the low beam filament (lower right-hand side in the case of keep-right traffic, lower left-hand side in the case of keep-left traffic), or right below thereof.
In the drawings, reference numeral 6 denotes a shade. The shade 6 is secured onto the reflector 4 and covers the light source bulb 5 at the front thereof, for the purpose of blocking the light from the low beam filament 51 and from the high beam filament 52 from directly entering an ineffective portion (a portion that does not directly contribute to the light distribution of the headlamp) 42 of the reflector 4 and the lens 2. Reference numeral 60 denotes a rubber cap. The rubber cap 60 is fitted detachably between a base of the light source bulb 5 and a rear opening of the lamp housing 1 by means of a fitting cap 61, thereby to keep the inside of the light room 3 water-tight.
When the low beam filament 51 of the automobile headlamp described above is turned on, light from the low beam filament 51 is reflected on the entire surface of the reflecting surface 40, and the reflected light is radiated through the lens 2 to the outside in a predetermined low beam light distribution pattern LP as shown in FIG. 18. On the other hand, when the high beam filament 52 is turned on, light from the high beam filament 52 is reflected on the entire surface of the reflecting surface 40, and the reflected light is radiated through the lens 2 to the outside in a predetermined high beam light distribution pattern HP as shown in FIG. 19.
In this way, the predetermined low beam light distribution pattern LP and the predetermined high beam light distribution pattern HP are formed by the control of all-surface reflection light distribution of the reflecting surface 40.
The predetermined low beam light distribution pattern LP and the predetermined high beam light distribution pattern HP described above refer to light distribution patterns in conformity with the European Light Distribution Standard ECEReg. or an equivalent regulation (for example, model recognition standard for vehicles sold in Japan), North American Light Distribution Standard FMVSS, etc.
The low beam light distribution pattern LP described above is made to comply with light distribution standard so that dazzling light is restricted. As a result, the low beam light distribution pattern LP described above has such a beam boundary 71 that does not annoy the driver of an oncoming vehicle 7 and a pedestrian 70 on the right road edge as shown in FIG. 18. The beam boundary 71 consists of a horizontal line portion 72 extending from the left end to near the center and located a little below the horizontal line HL-HR determined to avoid dazzling the driver of the oncoming vehicle 7, a mildly sloped line portion 73 that goes up from the horizontal line portion 72 at substantially the center toward the right at a small angle, 15.degree. for example, to make it possible to recognize the pedestrian 70 on the right road edge without dazzling the pedestrian 70 on the right road edge, and a sloped line portion 74 that goes down from the mildly sloped line portion 73 rightward to join the horizontal line portion 72. There is no standard related to the maximum luminous intensity in the low beam light distribution pattern LP.
For the high beam light distribution pattern HP described above, on the other hand, there are light distribution standards specified for the maximum luminous intensity and maximum luminous intensity zone, etc. As a result, the high beam light distribution pattern HP described above has a hot zone HZ (maximum luminous intensity zone including a point of maximum luminous intensity) in the central portion as shown in FIG. 19. The values of maximum luminous intensity specified in the European Light Distribution Standard ECEReg. is from 48 to 240 lx (1 lx=625 cd measured on a screen at a distance of 25 m), while the luminous intensity at an intersect H-V of the horizontal line HL-HR and the vertical line VU-VD is 80% of the maximum luminous intensity or higher (model recognition).
For the automobile headlamp described above, it is important to be capable of achieving good low beam light distribution pattern LP and high beam light distribution pattern HP.
In the automobile headlamp described above, the low beam filament 51 and the high beam filament 52 are disposed close to each other as shown in FIG. 20 and FIG. 21. Consequently, when the low beam filament 51 is turned on, a part L of the light from the low beam filament 51 illuminates a part of the high beam filament 52, namely an irradiated portion 520, and is reflected thereon. Reflection on the irradiated portion 520 of the high beam filament 52 has such an effect as if the irradiated portion 520 of the high beam filament 52 is lit with a low voltage simultaneously with the low beam filament 51. The irradiated portion 520 of the high beam filament 52 appears as a virtual image 86 in the low beam light distribution pattern LP as indicated by the shaded portion in FIG. 23, due to the maximum luminous intensity zone forming portion 85 (portion indicated by the solid line in FIG. 22) of the reflecting surface 40. The irradiated portion 520 of the high beam filament 52 described above does not make the virtual image 86 in portions other than the maximum luminous intensity zone forming portion 85 of the reflecting surface 40, since the light is diffused therein.
In FIG. 22, first quadrant 81, second quadrant 82, third quadrant 83 and fourth quadrant 84 are quadrants of the reflector 4 in front view. The maximum luminous intensity zone forming portion 85 tends to form a fan shape located below the horizontal line HR-HL, in many cases. At points A and B of the maximum luminous intensity zone forming portion 85, a light distribution pattern as shown in FIG. 23 is obtained. That is, light distribution patterns 87A, 87B indicated by solid lines are obtained with the low beam, and light distribution patterns 88A, 88B indicated by broken lines are obtained with the high beam. Since the automobile headlamp forms the predetermined low beam light distribution pattern LP and the predetermined high beam light distribution pattern HP by means of the control of all-surface reflection light distribution of the reflecting surface 40, the light distribution patterns 87A, 87B and the light distribution patterns 88A, 88B obtained at the points A and B of the maximum luminous intensity zone forming portion 85 have the same or similar shapes and are adjacent to each other as shown in FIG. 23, while the light distribution patterns 88A, 88B of the high beam are located above the light distribution patterns 87A, 87B of the low beam.
As a consequence, when the low beam filament 51 is turned on, the virtual image 86 of the irradiated portion 520 of the high beam filament 52 appears above the beam boundary lines 71, 72 and 73 of the low beam light distribution pattern LP as indicated by the shaded portion in FIG. 23. The virtual image 86 may appear as virtual image glare (glaring light) VIG (verified with 0.4 and 0.7 [lx] lines) at a point (or zone) GP of the European Light Distribution Standard ECEReg. where glaring light is strictly limited as shown in FIG. 24, due to the positional relationship between the low beam filament 51 and the high beam filament 52.
FIG. 24 shows isocandela diagrams measured on a screen located at a distance of 25 m. The isocandela diagrams are lines of 0.4, 0.7, 1.6, 4, 10, 16 and 25 [lx] (1 lx=625 cd), from the outermost one inward. In the isocandela diagrams of FIG. 24, 5L represents 5.degree. on the left and 5R represents 5.degree. on the right.
An application for an invention of automobile headlamp to eliminate the virtual image glare VIG described above (disclosed in Japanese Unexamined Patent Publication No. Hei 9-237504) was previously filed. The automobile headlamp (disclosed in Japanese Unexamined Patent Publication No. Hei 9-237504) has a low beam filament and a high beam filament separated by a shading hood such as an H4 valve to eliminate the virtual image glare VIG described above.
However, the automobile headlamp (disclosed in Japanese Unexamined Patent Publication No. Hei 9-237504) is not capable of effectively utilize near 100% of the light incident on the reflecting surface of the reflector because about 30 to 40% of the light incident on the reflecting surface of the reflector is cut off.